So I received my 50A last Tuesday and have been playing with it since. I haven't truly tested it as I've been too busy, but in general...a great lens. In good light the AF is hitting consistently and in low light the AF is as good as any other lens. Whereas I thought the AF on the 35A was a bit slow and noticed misses. Not so far with the 50A. The AF has been fast and accurate.
A few pics (both unaltered except for size reduction):
50A on 5DIII at 1/160 (moving cat), f/1.4, ISO 10,000 (testing the side AF points)
50A on 5DIII, 1/1,250, f/1.6, ISO 100
Here is a near 100% crop of the image above.
Anyway, just wanted to report back. I will continue to shoot with it to get used to the 50A, but so far, excellent.